Titolo della tesi: Multi-disciplinary design and multi-objective optimization of solid- and liquid- rocket based launch vehicles
Nowadays there is a tremendous competitiveness in the space sector, especially in the production
of new launch vehicles. Launch Vehicle design is a complex topic, because it requires the knowledge
of different disciplines such as propulsion, structures, aerodynamics, trajectory and controls, which
are strongly coupled between each others. Therefore, Multidisciplinary Design Optimization is the
correct approach to study and develop new launch vehicle configurations. Each discipline requires
the adoption of a proper engineering model to accurately describe its physic. Many researches have
been carried out on launch vehicle design optimization. However, the exploitation of finite element
model and computational fluid dynamics inside an optimization loop is still not common due to the
huge computational time required to perform a structural and an aerodynamic analysis.
This thesis proposes a methodology for a fast and effective multidisciplinary design optimization
using a high fidelity structural model generator, surrogate and reduced order models to accelerate
the phase A of development of new launch vehicles, balancing accuracy and computational time.
Indeed, the use of finite element surrogate models together with the real finite element solver
enhances the process of identifying the optimal design by enabling reduction in the running time
of the optimization procedure, making the finite element analysis suited for conceptual studies.
While, the use of a reduce order model for aerodynamic permits to complete avoid computational
fluid dynamics calculation inside the optimization loop.
More specifically, it is developed a procedure which, starting by a target payload and mission,
calculates the optimal propellant distribution between the stages in order to minimize the launch
vehicle mass. Then, once defined the mass budget and the external geometry, the trajectory up
to target orbit is evaluated and consequently the flight loads necessary to carry out the structural
analysis using both a refined finite element model and its surrogate. The multidisciplinary design
optimization procedure is managed in an advanced optimization environment in order to find the
best values of design variables that minimize or maximize the cost functions while respecting the
mission constraints. In order to validate this methodology, two launch vehicle configurations have
been studied: a three stages solid- and a two stages liquid- rocket based launch vehicle. On the three
stages configuration have been firstly carried out a structural optimization and after the complete
multidisciplinary optimization considering single and multiple objectives. Instead on the two stages
has been performed a complete multidisciplinary design optimization cycle with two separated
objectives.